This invention relates to the art of manufacture of field emission displays, and in a specific application, to the fabrication of patterned phosphor screens for high resolution displays. More specifically, the present invention relates to a black matrix material for such displays, and to a black matrix material which adheres to the interstitial regions between light-emitting phosphor pixels of a field emission display.
Many devices, such as computers and televisions, require the use of a display screen. Some of these devices, such as laptop computers, require a lightweight, portable screen as a display screen. Currently, such screens typically use electroluminescent or liquid crystal display technology. A promising technology to replace these types of screens is the field emission display (FED).
Field emission displays typically include a generally planar substrate having an array of projecting emitters. In many cases, the emitters are conical projections integral to the substrate. Typically, the emitters are grouped into emitter sets where the bases of the emitters in each set are commonly connected.
A conductive extraction grid is positioned above the emitters and driven with a voltage of about 30-120 V. The emitter sets are then selectively activated by providing a current path from the bases to the ground. Providing a current path to ground allows electrons to flow from the emitters in response to the extraction grid voltage. If the voltage differential between the emitters and extraction grid is sufficiently high, the resulting electric field extracts electrons from the emitters.
Field emission displays also include display screens mounted adjacent the substrates. The display screens are formed from glass plates coated with a transparent conductive material to form an anode biased to about 1-2 kV. A cathodoluminescent layer covers the exposed surface of the anode. The emitted electrons are attracted by the anode and strike the cathodoluminescent layer, causing the cathodoluminescent layer to emit light at the impact site. The emitted light then passes through the anode and the glass plate where it is visible to a viewer.
The brightness of the light produced in response to the emitted electrons depends, in part, upon the rate at which electrons strike the cathodoluminescent layer, which in turn depends upon the magnitude of current flow to the emitters. The brightness of each area can thus be controlled by controlling the current flow to the respective emitter set. By selectively controlling the current flow to the emitter sets, the light from each area of the display can be controlled and an image can be produced. The light emitted from each of the areas thus becomes all or part of a picture element or xe2x80x9cpixel.xe2x80x9d For a general overview of FED technology, see D. A. Cathey, Jr., xe2x80x9cField Emission Displays,xe2x80x9d Information Display Vol. 11, No. 10, pp, 16-60, October 1995, incorporated herein by reference in its entirety).
The manufacture of a FED presents several technical challenges. For example, application of phosphor to a conductive surface may involve the use of photoresist masks, as described in, for example, U.S. Pat. No. 4,891,110 to Libman, et al., which patent is incorporated herein in its entirety by reference. The use of this photoresist mask may cause some problems. As described in Libman et al., the photoresist is fixed in certain areas over a conductive surface, the unfixed photoresist is then removed by a wash (using, for example, water) and the exposed conductive surface is subjected to a cataphoretic bath to apply a phosphor to the conductive surface. After that application, the fixed photoresist material must be removed, which is accomplished in the field emission display art by way of washing with, for example, a hydrogen peroxide solution. Such washing involves mechanical agitation, which can dislodge particles of phosphor, resulting in unacceptable displays. This quality problem becomes even more critical as phosphor spot size or line width shrinks to achieve higher resolutions products.
To provide contrast in ambient light, a dark matrix material may be placed in the interstitial regions between the phosphor pixels. Unfortunately, many potential matrix materials have significant disadvantages when utilized under conditions associated with the manufacture of an FED. For example, di-aqueous graphite (DAG) tends to burn when heated in the presence of oxygen. Furthermore, DAG is conveniently used only in a bake-on/lift-off process, which is not feasible for use in the manufacture of high resolution or small area FEDs. Manganese carbonate, which is light in color upon initial deposit onto a display, tends to turn brown when subjected to elevated temperature under vacuum conditions (see Libman et al.). Such browning of manganese carbonate adversely effects contrast of the FED.
Accordingly, there is a need for a method and system for manufacture of field emission displays that will not mechanically agitate the phosphor during removal of photoresist material. Furthermore, there is a need in the art for a matrix material which remains black after being subjected to conditions associated with FED manufacture, particularly at elevated temperatures under vacuum. There is also a need for a black matrix material which may be applied by deposit techniques suitable for FED manufacture. The present invention fulfills these needs and provides further related advantages.
According to one embodiment of the present invention, a method is provided for producing high resolution displays. In brief, the present invention is directed to a black matrix material for adherence to the interstitial regions between light-emitting phosphor pixels of a field emission display. The black matrix material is selected from boron carbide, silicon carbide, tungsten carbide, vanadium carbide, and mixtures thereof. Such materials remain black when subjected to FED manufacturing conditions, and are both chemically inert and stable, making them particularly well suited within the practice of this invention.
In one embodiment of this invention, a method for manufacturing a faceplate for an FED is disclosed. The method involves depositing, preferably electrophoretically, the black matrix material on at least a portion of the faceplate. Prior to deposit, the faceplate may be patterned with a photoresist to expose only those areas of the faceplate on which the black matrix material is to be deposited. After depositing the black matrix material, the photoresist may be removed. A new photoresist is then patterned to expose only those areas of the faceplate on which the phosphor is to be deposited, followed by depositing phosphor in those exposed areas. After deposit of the black matrix material and phosphor, an appropriate binder may be employed, followed by successive baking steps. The resulting faceplate may then be used in the assembly of an FED.
In another embodiment, a method is disclosed for depositing a black grille on a faceplate of an FED by contacting the faceplate with an electrophoresis solution containing the black matrix material, and electrophoretically depositing the black matrix material on at least a portion of the faceplate. In this embodiment, the faceplate may again be patterned with a suitable photoresist prior to deposition of the black matrix material.
In another embodiment, a composition for electrophoretically depositing a black grille on a faceplate is disclosed, wherein the composition comprises the black matrix material, and preferably one or more of an electrolyte, an anti-agglomerating agent and a solvent.
In still a further embodiment, a faceplate having a black matrix material deposited thereon, as well as an FED comprising such a faceplate, are disclosed. Also disclosed are faceplates and FEDs made according to the above methods.
In yet another embodiment, a screen is disclosed. The screen comprises a substrate; a conductive layer carried by said substrate and covering a portion of said substrate; and a cathodoluminescent layer carried by said substrate and overlaying a region of said conductive layer. The cathodoluminescent layer includes: a first region defining a plurality of non-contiguous sub-regions, and a second region interstitial said sub-regions; said first region comprising light emissive substance and said second region comprising black matrix material.
Another embodiment of the invention provides for a field emission display. The field emission display comprises: an extraction grid having a plurality of openings; an emitter substrate including a plurality of emitters aligned with said plurality of openings; and a screen adjacent said extraction grid. The screen comprises: a substrate; a conductive layer carried by said substrate and covering a portion of said substrate; and a cathodoluminescent layer carried by said substrate and overlaying a region of said conductive layer. The cathodoluminescent layer comprises: a first region defining a plurality of non-contiguous sub-regions, and a second region interstitial said sub-regions; said first region comprising light emissive material and said second region comprising black matrix material; said sub-regions aligned to respective emitters.
In another embodiment of the invention, there is provided a display device. The display device comprises: a video signal generator capable of generating an image signal (e.g., a television or camcorder); an electronic controller driven by an image signal from said video signal generator, said electronic controller controlling an array of emitter control circuits; an emitter substrate including an array of emitters, said emitter control circuits individually coupled to individual emitters; an extraction grid having a plurality of openings, said openings aligned with said array of emitters; and a screen adjacent said extraction grid. The screen comprises a substrate; a conductive layer carried by said substrate and covering a portion of said substrate; and a cathodoluminescent layer carried by said substrate and overlaying a region of said conductive layer. The cathodoluminescent layer includes: a first region defining a plurality of non-contiguous sub-regions, and a second region interstitial said sub-regions; said first region comprising phosphor pixels and said second region comprising black matrix material.
These and other aspects of this invention will become apparent upon reference to the attached figure and the following detailed description.